The present invention relates to a sheet opening/closing and spreading apparatus. Particularly, the invention is concerned with a ventilating apparatus which opens and closes an opening formed at a suitable position in a roof surface, a side face or a gable end face of a greenhouse or is concerned with a sheet opening/closing and spreading apparatus suitable for opening and closing a heat retaining or light shielding sheet in a greenhouse.
Generally, in a greenhouse called a vinyl house which is used for the growth of plants, for example, a large number of arch pipes are erected on the ground and support rods and sheet retaining frames are disposed in a horizontal direction intersecting the arch pipes to constitute a framework, then a transparent or translucent sheet formed of a synthetic resin for example is spread manually on the said framework through the sheet retaining frames.
In the above greenhouse, an opening is formed at a suitable position in a roof surface, a side face or a gable end face and is opened and closed manually with use of a sheet to effect ventilation.
In the above greenhouse, a heat retaining or light shielding sheet is disposed at an upper or middle position and is opened and closed manually to adjust the interior temperature or allow the sunlight to be radiated directly to plants or cut off the sunlight.
Or a light shielding sheet is superimposed on the sheet which has been spread over the framework and is opened and closed manually to permit or cut off a direct radiation of sunlight for the interior of the greenhouse, thereby adjusting the interior temperature or the amount of sunlight radiated directly to plants.
When a sheet is to be spread over the framework as mentioned above, first the sheet is put on the framework manually and is then fixed at arbitrary positions into a sheet retaining frame of, for example, a dovetail shape through an elastic, retaining linear member.
When the interior of the greenhouse is to be ventilated, for example, the upper end of a sheet is fixed to the upper end of an opening through such sheet retaining frame and linear member as referred to above, while the lower end of the sheet is wound round a pipe extending in the direction traversing the sheet covering direction, and the said pipe is rotated manually or by means of a motor or the like, thereby winding the sheet onto the pipe from below to above and allowing the opening to be opened. Conversely, by winding back the thus-wound sheet from above to below, the opening is closed.
In the same manner as in the above ventilating mechanism, a heat retaining or light shielding sheet is opened and closed. That is, one end of the sheet is fixed to the framework or a support rod disposed in the interior, while the opposite end thereof is wound round a pipe, and the pipe is rotated manually or by means of a motor to take up the sheet, allowing an opening to be formed at a predetermined position. Conversely, upon winding back of the sheet, the sheet is spread at the predetermined position.
The above mechanism for spreading sheet manually over the greenhouse framework, the ventilating mechanism which performs winding up and winding back of sheet, and the heat retaining and light shielding mechanism which also performs winding up and winding back of sheet, do not involve any special defect, but involve the following points to be improved.
First, for the sheet spreading mechanism, it is desired that the following points be remedied.
(1) For fixing the spread sheet onto the framework, it is necessary that a sheet retaining frame of a dovetail groove shape be secured to vertical support rods such as arch pipes, thus resulting in an increase in the number of components, and it is difficult to effect assembly, which is disadvantageous in point of machinability, assembling performance and economy. Besides, for fixing the sheet to the sheet retaining frame, the sheet is drawn up manually over the whole framework in advance and is then fixed to the sheet retaining frame, so it is impossible to effect the sheet spreading work automatically, and the manually spreading work is very troublesome and difficult. Particularly, in the case where the fixing position is on the roof surface or an upper position of a side face or gable end face, the sheet fixing work is performed at an elevated place and there is a danger that the worker may fall. Further, in the event a sudden gust of wind should blow during the sheet fixing work at such an elevated position, the sheet may be flapped, blown up, or blown off.
(2) Likewise, when fixing the sheet to the sheet retaining frame, it is necessary to pull the sheet uniformly or pull one end thereof forcibly so as to prevent the occurrence of wrinkles or concaves and convexes. But this pulling work is difficult and requires a large force or may injure the workers' hands.
(3) Even after fixing the sheet to the sheet retaining frame and spreading, it is necessary that bands be applied onto the sheet to prevent the sheet from being flapped partially with wind for example. Thus, the number of components required increases and the band mounting work is difficult and troublesome.
(4) With the sheet once spread over the framework and in the event a strong wind or a sudden gust of wind is blown against the sheet due to a typhoon for example, the sheet cannot immediately be removed from the framework and hence the greenhouse itself may be blown off or damaged together with the framework.
Secondly, for the foregoing ventilating mechanism, it is desired that the following points be remedied.
(a) In the case where the ventilating mechanism is disposed in a lower opening formed in a side face or gable end face of the greenhouse, since the sheet is wound up from below to above, if a pipe for winding up the sheet while closing the opening is located near the ground, snow will accumulate on the pipe portion and it is required to remove the snow before winding up the sheet in winter. Besides, if the snow freezes, the ventilating operation cannot be started at once, and it is likely that the sheet may be damaged or the pipe may be bent due to the weight of the snow.
(b) At the time of winding up or winding back the sheet, the sheet is rubbed against the framework and may be damaged. Besides, when the sheet is wound up, dust, water and snow adhered to the sheet are also wound up together with the sheet, so that the sheet is stained. In this case, if the dust is hard and large or if volcanic ash, sand or earth is wound up, the wind-up and wind-back operation becomes difficult and the sheet may be broken due to rubbing.
(c) With the sheet wound up and the opening left open, the sheet is wound up many turns on the pipe, like a bundle, so if the sheet is allowed to stand in this state, rain water may get into the bundle-like sheet or snow will accumulate thereon, thus resulting in that not only the wind-back operation becomes difficult but also the sheet stain becomes conspicuous and may cause the occurrence of mold.
(d) Since the sheet is wound up from below to above for opening an opening, if the opening is formed in the lower end portion of a side face close to the ground, wind or cold air will enter the interior of the greenhouse upon wind-up of the sheet, which is not desirable for the growth of small seedlings. Therefore, it is necessary that a sheet called a dead sheet be spread over a side face near the ground to prevent such entry of wind or cold air. Thus, in building a greenhouse, such a ventilating mechanism is inferior in assembling performance, machinability and economy.
(e) Since the sheet is wound round a pipe extending across the sheet, if the framework is bent or deflected, the pipe cannot be kept horizontal, thus giving rise to a fear that the sheet may be wound inclinedly on the pipe or the pipe may become immovable or the sheet may be damaged.
Thirdly, in the same manner as in the above ventilating mechanism, the heat retaining and light shielding mechanism, which performs sheet winding up and winding back operations, involves the drawback that the sheet rubs and is broken or the stain such as dust adhered to the sheet is wound up together with the sheet, causing stain or breakage of the sheet.
In view of the above-mentioned points it is an object of the present invention to provide a sheet opening/closing apparatus capable of being utilized as any of sheet spreading mechanism, ventilating mechanism, and heat retaining and light shielding mechanism, in a greenhouse, capable of performing operations automatically, superior in all of working efficiency, assembling performance and economy, further capable of keeping sheet stain and breakage to a minimum, and exerting no bad influence on the growth of plants.